The Collaborative International Dictionary of English v.0.48:

Commando \Com*man"do\, n. [D. See Command, v. t.]
   1. In South Africa, a military body or command; also,
      sometimes, an expedition or raid; as, a commando of a
      hundred Boers.

            The war bands, called commandos, have played a great
            part in the . . . military history of the country.
                                                  --James Bryce.
      [Webster 1913 Suppl.]

   2. a usually small military unit trained to perform special
      missions, often behind enemy lines, and usually employing
      hit-and-run tactics. Such units often have the destruction
      of fixed targets, such as enemy installations, as their
      mission, in contrast to normal combat units which engage
      the enemy army directly.
      [PJC]

   3. a member of a commando[2] unit.
      [PJC]

WordNet (r) 3.0 (2006):

commando
    n 1: a member of a military unit trained as shock troops for
         hit-and-run raids [syn: commando, ranger]
    2: an amphibious military unit trained for raids into enemy
       territory